If you're going to go AMD, then you ought to look into AM3+ boards. The 550ti is underpowered at 1080p, and even if those boards could SLI, the Tom's editors say they microstutter when set up as such. SO, I'd recommend going with an AM3+ mobo, and putting as much money as you can into the GPU, grab a 560(ti) or a 6970 if you can, along with a board that can SLI/CF.